1. Field
Example embodiments relate to a semiconductor laser diode and a method of fabricating the same. Example embodiments also relate to a semiconductor laser diode having a wafer-bonded structure and a method of fabricating the same.
2. Description of the Related Art
Despite being small, semiconductor laser diodes may have lower threshold currents during laser oscillation than other laser devices. Semiconductor laser diodes may be widely applied in the field of telecommunications. They also may be applicable as devices with improved speed for data transmission or certain read/write functions in players using optical discs.
For example, gallium nitride (GaN)-based laser diodes may allow using wavelengths from the ultraviolet region to the visible-green region of the electromagnetic spectrum. GaN-based laser diodes may be applicable in various areas, including storage/reproduction devices using increased density optical information, laser printers with increased resolution, and projection televisions.
GaN-based laser diodes may have a structure including an n-AlxGa1-xN layer, where 0≦x≦1, an indium gallium nitride (InGaN) active layer, and a p-AlxGa1-xN layer (an optical guide), where 0≦x≦1. The p-AlxGa1-xN layer may be formed in a multi-layered structure including an electron shield layer, a p-waveguide layer, a p-clad layer, and a p-contact layer.
However, the InGaN active layer may be grown at a temperature less than about 800° C., while the p-AlGaN layer formed above the InGaN active layer may be grown at a temperature in excess of about 900° C. Because the p-AlGaN layer may have a thickness of about 0.5 μm or more, the growth of the p-AlGaN layer may take longer than the other layers. When the p-AlGaN layer is grown at about 900° C. or more, the InGaN active layer (with an increased composition ratio of indium (In)) may be exposed to elevated temperature conditions for longer periods of time. Under these conditions, the InGaN active layer may be degraded, and/or a local segregation of In may take place.
Degradation and local segregation may often become severe in GaN-based laser diodes with long wavelengths extending into the visible-green region of the spectrum. More specifically, as the composition ratio of In in the InGaN active layer increases, the wavelength of emitted light may be lengthened and the growth temperature of the InGaN active layer may decrease. For those GaN-based laser diodes with long wavelengths and In-based active layers grown at lower temperatures, the growth temperature difference between the In-based active layer and the p-AlGaN layer may be increased. Accordingly, the degradation of the In-based active layer and/or the local segregation of In may become more severe as compared to other diodes.
If the growth temperature of the p-AlGaN layer is lowered to prevent or reduce the degradation of the active layer, the increased doping concentration of magnesium (Mg) may be limited. As the number of p-AlGaN layers formed above the active layer increases, lattice defects may also occur more frequently.